Photographs of U.S. triatomine species, Triatoma and Paratriatoma. The image size relative to the scale bar represents the average length of each species. Photographs for T. incrassata , T. recurva , and P. hirsuta were unavailable . All photographs are by S. Kjos. 

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... initiatives (220, 269). Serological screening of blood components for T. cruzi is now compulsory in all but one of the countries in Latin America where the disease is endemic, and the prevalence of infection in screened donors has decreased substantially (196, 269). Nevertheless, Chagas’ disease screening coverage by country was estimated to vary from 25% to 100% in 2002, and the risk of transmission, though much decreased, has not been eliminated (269). The residual risk in Latin America where screening has been implemented is estimated to be 1:200,000 units (269, 308). Organ-derived transmission. Uninfected recipients who re- ceive an organ from a T. cruzi -infected donor may develop acute T. cruzi infection. However, transmission is not universal; in a series of 16 uninfected recipients of kidneys from infected donors, only 3 (19%) acquired T. cruzi infection (238). Nine- teen instances of transmission by organ transplantation have been documented in the literature (13 kidney, 1 kidney and pancreas, 3 liver, and 2 heart transplants) (16, 61, 66, 79, 99, 101, 157, 238, 279). The risk from heart transplantation is thought to be higher than that from kidney or liver transplantation (65). One case of transmission through unrelated cord blood transplantation has been reported (104). Oral transmission. Recently, increasing attention has focused on the oral route of T. cruzi transmission; several outbreaks attributed to contaminated fruit or sugar cane juice have been reported from Brazil and Venezuela (28, 82, 208). Most outbreaks are small, often affecting family groups in the Amazon region, where the palm fruit a ̧aí is a dietary staple that appears to be particularly vulnerable to contamination, perhaps from infected vectors living in the trees themselves (74, 208). The largest reported outbreak to date led to more than 100 infections among students and staff at a school in Caracas; locally prepared guava juice was implicated (82). The epidemiology of vector-borne T. cruzi is closely linked to the biological and ecological characteristics of local vectors and mammalian reservoir hosts. Triatomines of both sexes must take blood meals to develop through their nymphal stages to adults, and females require a blood meal to lay eggs. Thus, nymphs and adults of either sex may be infected with T. cruzi , but infection rates increase with increasing vector stage and age. Most domestic triatomine species feed nocturnally and are able to complete their blood meal without waking the host (169). The major Latin American vectors defecate during or immediately after taking a blood meal. T. cruzi infection is transmitted to wild mammals by sylvatic triatomine species; these bugs often colonize the nests of ro- dent or marsupial reservoir hosts (169, 311). Sylvatic triatomine adults may fly into human dwellings because of attraction by light and cause sporadic human infections (74). Domestic transmission cycles occur where vectors have become adapted to living in human dwellings and nearby animal enclosures; domestic mammals such as dogs, cats, and guinea pigs play important roles as triatomine blood meal sources and T. cruzi reservoir hosts (69, 124, 131). Some triatomine species can infest both domestic and sylvatic sites and may play a bridging role (192). There are more than 130 triatomine species in the Americas, many of which can be infected by and transmit T. cruzi (169, 311). However, a small number of highly domiciliated vectors are of disproportionate importance in the human epidemiology of disease (Table 2) (311). The domestic environment provides abundant blood meal sources, and poor quality housing with adobe or unfinished brick walls provides crevices and other diurnal hiding places for triatomines (170, 201). Thatch roofs provide an attractive habitat for some species (117). In communities where the disease is endemic, 25 to 100% of houses may be infested, and a house and its immediate sur- roundings may support large colonies of juvenile and adult bugs (170, 201, 230). In areas of the Amazon where deforestation and human immigration have occurred, tree-dwelling sylvatic triatomine populations have survived and rebounded by adapting to new vertebrate host species (2). These opportunistic vertebrates (opossums and rodents) are competent Chagas’ disease reservoirs and are acclimated to living in close proximity to humans where remnant vegetation is located. The concentration of triatomines and vertebrate reservoirs in the peridomestic realm has lead to increased interactions between sylvatic triatomine species and humans in deforested areas of the Amazon and Panama and to an apparent increase in the incidence of Chagas’ disease in humans (4, 244). Eleven species of triatomine bugs have been reported from the United States: Triatoma gerstaeckeri , T. incrassata , T. indictiva , T. lecticularia , T. neotomae , T. protracta , T. recurva , T. rubida , T. rubrofasciata , T. sanguisuga , and Paratriatoma hirsuta (Fig. 1 and Table 3). Triatomines are present across the southern half of the country, distributed from the Pacific to Atlantic coasts (Fig. 2). One species ( T. rubrofasciata ) is found in Hawaii. A high degree of polymorphism has been noted in several species across their geographic ranges, particularly T. protracta , T. rubida , and T. sanguisuga , resulting in proposed subspecies classifications (249, 251, 254, 296). However, due to the recognition of morphological intermediates across some subspecies groups and the absence of supporting data (e.g., paired molecular and morphological studies), these subspecies have not been universally accepted as valid taxonomic groups (110, 169). All U.S. species except T. rubrofasciata and T. sanguisuga have been collected in Mexico; the distribution of T. sanguisuga likely extends into northeastern Mexico as well (255). A review of the published literature from 1939 to 2010 resulted in reports of wild-caught triatomine bugs from 262 counties in 28 states. The greatest species diversity occurs in the southwest, particularly Texas, Arizona, and New Mexico. More specifically, high species diversity is concentrated in south-central Arizona and southwestern Texas, where up to five species have been recorded in a single county (Fig. 2). T. cruzi -infected specimens have been reported from 10 states, predominantly from counties in the Southwest (Fig. 3A). All species except T. incrassata and P. hirsuta have been found naturally infected with T. cruzi (Fig. 3B to L). County-level maps (Fig. 2 and 3) reflect in part where collection efforts have been focused over the past 70 years. There is no evidence of a temporal or spatial trend in the published reports to suggest any recent migration of species into or within the United States. The county maps do not necessarily reflect triatomine population densities or provide a complete representation of their distributions. Rather, the maps more likely provide an indication of where the bugs have been considered a pest to humans or animals and where field efforts were concentrated as a consequence or where specimens were collected coincidentally by researchers studying other animal systems (i.e., reports based on museum specimens). Collection records are more comprehensive in the southwestern states and Florida, with sparse records in the southeastern states. Early discovery of the association of U.S. triatomine bugs with Neotoma species of woodrats may have aided field research in the southwestern states, because woodrat species in this region build easily identifiable, above-ground dens. The absence of records in some areas of the southeastern United States may reflect a paucity of field studies or published records in those locations rather than being an indication of true absence of the bug. The detection of T. cruzi -infected wild mammals in many of these areas suggests the presence of the vectors. Additionally, recent efforts to model the geographic distribution of U.S. species based on the land cover, climate, and host composition of known collection sites indicate favorable habitat suitability in many of these unsurveyed or underreported regions (26, 137, 158, 259). Characteristics of each species are summarized in Table 3 and described in detail in the sections that follow. Triatoma gerstaeckeri (Stål). T. gerstaeckeri is one of the most frequently collected and tested species in the United States; 57.7% (1,038/1,800) of tested specimens were found to harbor T. cruzi . T. cruzi -infected specimens have been found in both Texas and New Mexico and in the majority of the counties where testing has been reported (Fig. 3B). Published reports from the 1930s to 1960s describe T. gerstaeckeri as a pest species of humans and livestock; the adult bugs were frequent invaders of rural houses in Texas, and reports of humans being bitten were common (217, 330, 332). Human encounters have been less frequently reported in recent decades (49, 151). Infected T. gerstaeckeri specimens were recently recovered from the residence of a child with acute Chagas’ disease in southern Texas (151). In northeastern Mexico, this species is considered an important Chagas’ disease vector due to its close association with human dwellings (184, 288). U.S. T. gerstaeckeri data derive predominantly from Texas, where the bug has been found in a wide variety of habitats. The species was collected from a rock squirrel burrow in a cave in the southeastern corner of New Mexico (341). Triatoma incrassata Usinger. T. incrassata is somewhat similar to T. protracta in size and general appearance of legs and head, but it has a distinctive abdominal margin which is largely yellow on the dorsal surface and entirely yellow on the ventral surface. It has been collected at lights in the two southern Arizona counties of Santa Cruz and Pima (Fig. 3C) (169, 255). The major mammalian hosts and T. cruzi infection prevalence for this species are unknown. Triatoma indictiva ...